A SECOND BA jet has been forced to make an emergency landing in the space of just 11 days due to ­suspected toxic oil fumes contaminating the cockpit.

The pilots of a Boeing 747 with 266 people on board had to wear oxygen masks to land the plane ­after passengers and crew ­became unwell at 33,000ft.

American Idol host Ryan ­Seacrest and his singer and actress girlfriend Julianne Hough were on board the jet.

It was less than an hour into a trip from Los ­Angeles to Heathrow on Thursday night when the captain became worried about a smell affecting crew and business class customers on the upper deck.

He initially turned around to go back to Los Angeles but changed his mind minutes later and radioed for ambulances to meet the aircraft at Las Vegas.

A number of passengers were treated by paramedics and all three pilots and four cabin crew were taken to hospital for check-ups.

One passenger said: “The pilots actually put on their oxygen and the other stewards were sick.”

British Airways said the aircraft has been taken out of service pending an investigation. It said early indications pointed to a “fault with the number three ­engine”.

The Sunday Express call for the fitting of toxic air detectors would seem a reasonable, common sense solution

There is growing concern among passengers and scientists about the dangers of toxic air on board commercial planes.

Many believe exposure can cause a debilitating long-term illness known as “aerotoxic syndrome”, which is often misdiagnosed by doctors due to a lack of expertise and awareness.

Concern centres on the way unfiltered air is sucked into the cabin and cockpit via a bleed pipe off the engines, where any oil leak at high temperatures can release dangerous compounds including toxic ­organophosphates.

The Sunday Express has called for air quality monitors to be fitted on commercial aircraft, but under current regulations, pilots have to rely on their noses to detect any fumes on board.

Last month, this newspaper ­revealed that two 46-year-old BA pilots had died within weeks of each other after years of complaints that toxic fumes had ruined their health.

Last week the Sunday Express also revealed how a BA flight from Heathrow to Philadelphia had been forced to land at a remote Canadian military base after a pilot was “incapacitated” due to suspected toxic fumes.

The plane in that ­incident, a Boeing 777, was also ­involved in an emergency “fume event” at Heathrow in 2009. On February 3 we reported how a former US government adviser feared fumes could lead to disaster, right.

BA declined to say when the faulty engine on the Boeing 747 had last been overhauled.

A spokesman said: “The engine’s maintenance programme would, of course, be in accordance with the manufacturer’s regulations. Safety is always our top priority.”

Ryan Seacrest and Jullanne Hough were on the plane forced to land

He apologised to Thursday night’s passengers, who remained in Las Vegas yesterday. “Customers are being rebooked on to alternative flights,” he said.

“The smell could only be smelt on the upper deck and 20 business class customers in that area were informed of the situation. There was no unusual smell on the main deck.”

Former pilot Captain John Hoyte, who founded the Aerotoxic Association after his health was ­affected, demanded industry action.

He said: “While the industry states ‘there is no evidence’, we’ve been recording toxic ‘fume events’ and the associated serious ill health from aircrew and passengers for nearly six years. No one has asked to see thetestimonies.

“The Sunday Express call for the fitting of toxic air detectors would seem a reasonable, common sense solution to alert aircrew to a hazardous condition.”

A Government commissioned study concluded in 2011 that cabin air was safe, but its results have been disputed.